ADS-B - aircraft position broadcasts
A signal by which an aircraft broadcasts its own position, altitude and identity. Overflight counts use it; small aircraft are often missing.
ADS-B (Automatic Dependent Surveillance - Broadcast) is a way of tracking aircraft in which the aircraft automatically broadcasts data from its own navigation equipment: position, pressure altitude, speed and identity. Air traffic control receives the signal, but so do ground receivers run by volunteers. Their records feed public flight tracking maps and flight archives.
Which aircraft broadcast ADS-B
- Only some must. Commission Implementing Regulation (EU) No 1207/2011 requires ADS-B for aircraft with a maximum take-off mass over 5,700 kg or a cruising speed over 250 knots flying under instrument flight rules (IFR). In practice these are airliners and larger business aircraft.
- Smaller aircraft on IFR flights need only a basic Mode S transponder, which does not broadcast position by itself. Flights under visual flight rules (VFR) are not covered by this requirement. Sport and ultralight aircraft, gliders and many helicopters are therefore missing from the data or appear only sometimes.
- State and military aircraft have special rules and exemptions in the regulation (Article 8), so military flights may also be missing.
How to read overflight data
- ADS-B altitude is pressure (barometric) altitude based on standard air pressure. It roughly matches height above sea level, not above the ground: for a house at 400 m above sea level, an aircraft reported at 1,500 m flies about 1,100 m above the roof.
- Volunteer receiver networks do not cover every area equally. A low-flying aircraft far from a receiver may not be picked up, so overflight counts are rather a lower estimate.
- The approach paths to an airport change with the wind direction and runway use, so individual days differ.
- Overflights are not a noise measurement. Airport noise is shown by the strategic noise map and the airport noise protection zone.
Frequently asked questions
Where do the overflight data in the Property Check come from?
From the flight archive of the adsb.lol community network, published under the open ODbL 1.0 licence. The Property Check calculates the average number of passes per day within 1 km of the house in two altitude bands, separately for day and night.
Want this information for a specific property?
Before you buy, we find, analyse and clearly present data about the place: land register, utilities from the operators, floods, zoning plan. An address is enough, within 48 hours, CZK 5,900.
The explanation is general and informative, not legal advice. The land register, the zoning plan and other official sources are binding.